Power supplies are customarily operated as stand-alone devices As a rule, they are fitted with a simple indicator contact. It can in this way be indicated whether the status of the power supply is currently undisturbed or faulty.
Power supplies typically convert a high voltage level on the input side, for example a 230V alternating voltage or a 400V alternating voltage, to a low voltage level, for example a direct voltage of 24V. By this means, consumers such as sensors, electronic controls, valves and pumps can be operated with a suitable voltage, without the need for a separate power supply for each individual consumer. Power supplies of this type are used on a large scale in production and automation engineering, for example.
A diagnostic unit for a power supply and a power supply fitted with a diagnostic unit are described in DE 103 55 613.3. The diagnostic unit monitors the power supply on the output side for an inadmissible deviation from a reference value of at least one parameter to be monitored. In the event of an inadmissible deviation from the reference value, the diagnostic unit records measurement values on the input side of the power supply in the period of time surrounding the inadmissible deviation in a time window. The diagnostic unit then files the relevant measurement values in a memory. The result is that the deviation of a parameter to be monitored which is caused by a fault on the mains side, for example an underrun of the output voltage, can be documented with certainty. In this way, it can be proven to an operator of the power supply that it is not the power supply but the superordinate power network which is failing to meet the requirements specified for operating power supplies. Network faults on the input and output side and equipment faults on the power-supply side can be recorded, interrogated and analyzed smoothly and promptly at low cost. In one embodiment, the diagnostic unit has a communication interface for reading out the memory. The memory comprising the measurement values can be read out via this interface and evaluated, for example on a linked personal computer with suitable software. Remote control is also possible via the communication interface of the diagnostic unit. Here, online measurement values can be transmitted to a linked personal computer and evaluated. The facility also exists for loading new firmware or new values for the parameters being monitored into the control unit of the diagnostic unit.